The present invention relates to a bar code reading device for reading bar code information from a bar code.
The bar code reading device projects light onto a bar code, receives light reflected from the bar code, converts width information of the bar code into time information, converts the time information into numerical values, and sequentially stores the numerical values as binary data into a memory by a DMA (direct memory access) method, for example (data gathering process). After the bar code binary data of one scan is stored into the memory, the binary data that is stored in the memory is analyzed to read bar code information (decoding process).
Where a single memory area is used for storing the binary data, the data gathering process and the decoding process are alternately carried out for the memory area. Where a plural number of memory areas or a memory area that is divided into a plural number of segments is used for storing the binary data, the data gathering process and the decoding process are concurrently carried out. More specifically, the data gathering process is carried out for one memory area or one segment, while the decoding process is carried out for another memory area or another segment.
Such a reading operation is usually repeated till the same bar code information is read two times or till a command to forcibly end the measurement is issued. When the same bar code information is read two times, the read bar code information is outputted. When the same bar code information is not read two times at the end of the measurement, an error signal is outputted.
Thus, in the conventional bar code reading device, the same bar code information is read two times, and the read bar code information is outputted. Accordingly, where a read rate (the ratio of a number of successful readings to a number of actual reading operations) is high, the necessary bar code information can be gained through the first two reading operations. Where the read rate is low, many reading operations are required for gaining the same bar code information two times. In this case, it is impossible to know the reason why the read rate is low, although the bar code information can be gained.
Usually, the bar code reading device is designed so as to have a single function to read out bar code information. Further, there is a physical limit in the memory capacity of a memory used. Accordingly, every time the decoding process ends, the memory area is set free for the storage of the next binary data. For this reason, when the same bar code information is read out two times and the measurement normally ends, the binary data normally read out is stored in the memory area of the memory. If the measurement by the bar code reading device is forcibly ended at an arbitrary time point, the binary data read out at that time point is stored into the memory area of the memory.
The data left in the memory area of the memory at the end of the measurement is either of two types of binary data. Therefore, when the bar code information is not read out, it is impossible to subsequently verify the reason why the reading of the bar code information failed by analyzing the data left in the memory area of the memory.
A bar code verifying device which reads out a still bar code and carefully evaluates the bar code information of the bar code is used. The bar code verifying device is capable of inspecting a defective on the bar code, but cannot be used as a bar code reading device in production lines in a factory.
For this reason, it is inherently impossible to verify a defective occurring only in the bar code reading device actually used, and a read error occurring on the bar code being under measurement in the production line in a factory. Further, an error of the analog signal from the bar code reading device and an error in the optical system cannot be verified. In a case where three reading operations are performed but one of the reading operations fails, an operator cannot know the reason why the reading operation fails, and the fact that dust attaches to the bar code in the production line, for example.
Additionally, where the conventional bar code reading device is used, an operator cannot know reading states, such as a number of operations of reading the same bar code information and a read rate, during the measurement of the bar code.